#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
using namespace std;

int main()
{
    cout << R"(printf("Hello world!\n");)" << endl;
    cout << R"(cout << "Hello world!" << endl;)" << endl;
    printf("printf(\"Hello world!\\n\");\n");
    printf("cout << \"Hello world!\" << endl;");
}